1. Field of the Invention
The present invention relates to an image forming apparatus, information processing apparatus, image forming system, image position correcting method, recording media, and a computer-readable program that are applicable to a network image forming system having a function of reading images from documents and reproducing them on both sides of paper.
2. Description of Related Art
Recently, it has become very common to use monochromatic and color printers, copiers, and multi-function peripherals (MFPs) that form images from arbitrary image information. For example, a monochromatic digital copying machine has a scanner and an image forming section consisting of an exposing section, a developer, a photosensitive drum, and a fixing section.
A document is read by a scanner and its image is turned into binary data, or image information. The exposing section draws an electrostatic latent image on the photosensitive drum according to the image information after image processing. The developer applies black toner to the electrostatic latent image on the photosensitive drum to make it visible. The developed toner image is transferred from the photosensitive drum to a piece of paper and fixed to the paper by the fixing section. With this, an image can be formed on the paper fed from the paper tray.
It has also become very common to use copiers, printers, and MFPs that duplicate document images on both sides of paper (Double-Side Copy mode). The Double-Side Copy mode enables preparation of a cover for a hand-made booklet or the like. For example, an A3-Wide size paper is often used as a cover for a booklet made of A4 size paper sheets. A two-folded A3-Wide size paper sheet is slightly larger than an A4-size paper sheet. In the Double-Side Copy mode, the page position on one side of an A4-size paper sheet must be matched with the page position on the other side of the paper sheet for assurance of image formation quality.
Usually, such copiers, printers and MFPs are designed to form images at the same position on both sides of each piece of paper. In some cases, however, the printed images may not be at the expected positions on both sides of the paper because of heat shrinkage of paper and so on. To alleviate such displacement of images on both sides of paper, conventional printing and copying machines have employed a method of manually measuring the image displacement using rulers or the like, calculating a value to eliminate the displacement, and manually entering the value into the machine.
One conventional image forming apparatus writes positioning marks on both sides of paper, reads the mark on one side of the paper together with the mark on the other side of the paper through the paper using its scanner. Its information processor processes image data of these marks and detects a positional difference between them. The configuration of this image forming apparatus can remove or alleviate not only a positional difference between images on both sides of paper but also a magnification difference between them due to shrinkage and expansion of paper and can match the image forming positions on both sides of paper. One such apparatus is described, for example, in Japanese Non-examined Patent Publication 2003-173109 (e.g., Page 6, FIG. 1).
Recently, users of image forming apparatus such as copying machines with a double-side copying function have wanted to attach covers to hand-made booklets and leaflets. This leads to formation of images greater in size than the image readable area (or the maximum scan size) of the scanner of the image forming apparatus.
For example, an image forming apparatus such as a copier with a maximum scan size of A-3 may be requested to form images on A3-Wide size paper. However, it has been hard to correct the positional difference between positioning marks on both sides of the paper when the positioning marks are outside the image reading area of the scanner and cannot be detected.